A wireless communications device following the industry standard IEEE 802.11n may communicate over a channel with a bandwidth of 40 MHz (comprised of two contiguous 20 MHz channels), while older legacy devices may only be able to communicate over the 20 MHz channels. To allow both types of devices to operate cooperatively in the same network, an 802.11n device may receive a downlink transmission over a wide 40 MHz channel, but transmit its uplink acknowledgement simultaneously over each of the narrow 20 MHz channels that make up that wide channel. Since the legacy devices are able to receive and decode this acknowledgement over at least one of the narrow channels, this allows them to know their narrow channels are busy so they won't transmit an interfering signal during that time. However, if the downlink transmission is directed towards multiple 802.11n devices, they must transmit their acknowledgements sequentially to avoid interfering with each other. These sequential transmissions unnecessarily take up time on those channels that could otherwise be used by other devices.